test/loops/BinaryAsyncAction.java

/*
 * Written by Doug Lea with assistance from members of JCP JSR-166
 * Expert Group and released to the public domain, as explained at
 * http://creativecommons.org/publicdomain/zero/1.0/
 */

import java.util.concurrent.*;
import java.util.concurrent.atomic.*;

/**
 * AsyncActions that are always linked in binary parent-child
 * relationships. Compared to Recursive tasks, BinaryAsyncActions may
 * have smaller stack space footprints and faster completion mechanics
 * but higher per-task footprints. Compared to LinkedAsyncActions,
 * BinaryAsyncActions are simpler to use and have less overhead in
 * typical uasges but are restricted to binary computation trees.
 *
 * <p>Upon construction, a BinaryAsyncAction does not bear any
 * linkages. For non-root tasks, links must be established using
 * method <tt>linkSubtasks</tt> before use.
 *
 * <p><b>Sample Usage.</b>  A version of Fibonacci:
 * <pre>
 * class Fib extends BinaryAsyncAction {
 *   final int n;
 *   int result;
 *   Fib(int n) { this.n = n; }
 *   protected void compute() {
 *     if (n &gt; 1) {
 *       linkAndForkSubtasks(new Fib(n-1), new Fib(n-2));
 *     else {
 *       result = n; // fib(0)==0; fib(1)==1
 *       complete();
 *     }
 *   }
 *   protected void onComplete(BinaryAsyncAction x, BinaryAsyncAction y) {
 *     result = ((Fib)x).result + ((Fib)y).result;
 *   }
 * }
 * </pre>
 * An alternative, and usually faster strategy is to instead use a
 * loop to fork subtasks:
 * <pre>
 *   protected void compute() {
 *     Fib f = this;
 *     while (f.n &gt; 1) {
 *       Fib left = new Fib(f.n - 1);
 *       Fib right = new Fib(f.n - 2);
 *       f.linkSubtasks(left, right);
 *       right.fork(); // fork right
 *       f = left;     // loop on left
 *     }
 *     f.result = f.n;
 *     f.complete();
 *   }
 * }
 * </pre>
 */
public abstract class BinaryAsyncAction extends ForkJoinTask<Void> {
    private volatile int controlState;

    static final AtomicIntegerFieldUpdater<BinaryAsyncAction> controlStateUpdater =
        AtomicIntegerFieldUpdater.newUpdater(BinaryAsyncAction.class, "controlState");

    /**
     * Parent to propagate completion; nulled after completion to
     * avoid retaining entire tree as garbage
     */
    private BinaryAsyncAction parent;

    /**
     * Sibling to access on subtask joins, also nulled after completion.
     */
    private BinaryAsyncAction sibling;

    /**
     * Creates a new action. Unless this is a root task, you will need
     * to link it using method <tt>linkSubtasks</tt> before forking as
     * a subtask.
     */
    protected BinaryAsyncAction() {
    }

    public final Void getRawResult() { return null; }
    protected final void setRawResult(Void mustBeNull) { }

    /**
     * Establishes links for the given tasks to have the current task
     * as parent, and each other as siblings.
     * @param x one subtask
     * @param y the other subtask
     * @throws NullPointerException if either argument is null.
     */
    public final void linkSubtasks(BinaryAsyncAction x, BinaryAsyncAction y) {
        x.parent = y.parent = this;
        x.sibling = y;
        y.sibling = x;
    }

    /**
     * Overridable callback action triggered upon <tt>complete</tt> of
     * subtasks.  Upon invocation, both subtasks have completed.
     * After return, this task <tt>isDone</tt> and is joinable by
     * other tasks. The default version of this method does nothing.
     * But it may be overridden in subclasses to perform some action
     * (for example a reduction) when this task is completes.
     * @param x one subtask
     * @param y the other subtask
     */
    protected void onComplete(BinaryAsyncAction x, BinaryAsyncAction y) {
    }

    /**
     * Overridable callback action triggered by
     * <tt>completeExceptionally</tt>.  Upon invocation, this task has
     * aborted due to an exception (accessible via
     * <tt>getException</tt>). If this method returns <tt>true</tt>,
     * the exception propagates to the current task's
     * parent. Otherwise, normal completion is propagated.  The
     * default version of this method does nothing and returns
     * <tt>true</tt>.
     * @return true if this task's exception should be propagated to
     * this task's parent.
     */
    protected boolean onException() {
        return true;
    }

    /**
     * Equivalent in effect to invoking <tt>linkSubtasks</tt> and then
     * forking both tasks.
     * @param x one subtask
     * @param y the other subtask
     */
    public void linkAndForkSubtasks(BinaryAsyncAction x, BinaryAsyncAction y) {
        linkSubtasks(x, y);
        y.fork();
        x.fork();
    }

    /** Basic per-task complete */
    private void completeThis() {
        super.complete(null);
    }

    /** Basic per-task completeExceptionally */
    private void completeThisExceptionally(Throwable ex) {
        super.completeExceptionally(ex);
    }

    /*
     * We use one bit join count on taskState. The first arriving
     * thread CAS's from 0 to 1. The second ultimately sets status
     * to signify completion.
     */

    /**
     * Completes this task, and if this task has a sibling that is
     * also complete, invokes <tt>onComplete</tt> of parent task, and so
     * on. If an exception is encountered, tasks instead
     * <tt>completeExceptionally</tt>.
     */
    public final void complete() {
        // todo: Use tryUnfork without possibly blowing stack
        BinaryAsyncAction a = this;
        for (;;) {
            BinaryAsyncAction s = a.sibling;
            BinaryAsyncAction p = a.parent;
            a.sibling = null;
            a.parent = null;
            a.completeThis();
            if (p == null || p.compareAndSetControlState(0, 1))
                break;
            try {
                p.onComplete(a, s);
            } catch (Throwable rex) {
                p.completeExceptionally(rex);
                return;
            }
            a = p;
        }
    }

    /**
     * Completes this task abnormally. Unless this task already
     * cancelled or aborted, upon invocation, this method invokes
     * <tt>onException</tt>, and then, depending on its return value,
     * completees parent (if one exists) exceptionally or normally.  To
     * avoid unbounded exception loops, this method aborts if an
     * exception is encountered in any <tt>onException</tt>
     * invocation.
     * @param ex the exception to throw when joining this task
     * @throws NullPointerException if ex is null
     * @throws Throwable if any invocation of
     * <tt>onException</tt> does so.
     */
    public final void completeExceptionally(Throwable ex) {
        BinaryAsyncAction a = this;
        while (!a.isCompletedAbnormally()) {
            a.completeThisExceptionally(ex);
            BinaryAsyncAction s = a.sibling;
            if (s != null)
                s.cancel(false);
            if (!a.onException() || (a = a.parent) == null)
                break;
        }
    }

    /**
     * Returns this task's parent, or null if none or this task
     * is already complete.
     * @return this task's parent, or null if none.
     */
    public final BinaryAsyncAction getParent() {
        return parent;
    }

    /**
     * Returns this task's sibling, or null if none or this task is
     * already complete.
     * @return this task's sibling, or null if none.
     */
    public BinaryAsyncAction getSibling() {
        return sibling;
    }

    /**
     * Resets the internal bookkeeping state of this task, erasing
     * parent and child linkages.
     */
    public void reinitialize() {
        parent = sibling = null;
        super.reinitialize();
    }

    /**
     * Gets the control state, which is initially zero, or negative if
     * this task has completed or cancelled. Once negative, the value
     * cannot be changed.
     * @return control state
     */
    protected final int getControlState() {
        return controlState;
    }

    /**
     * Atomically sets the control state to the given updated value if
     * the current value is and equal to the expected value.
     * @param expect the expected value
     * @param update the new value
     * @return true if successful
     */
    protected final boolean compareAndSetControlState(int expect,
                                                      int update) {
        return controlStateUpdater.compareAndSet(this, expect, update);
    }

    /**
     * Attempts to set the control state to the given value, failing if
     * this task is already completed or the control state value would be
     * negative.
     * @param value the new value
     * @return true if successful
     */
    protected final void setControlState(int value) {
        controlState = value;
    }

    /**
     * Sets the control state to the given value,
     * @param value the new value
     */
    protected final void incrementControlState() {
        controlStateUpdater.incrementAndGet(this);
    }

    /**
     * Decrement the control state
     * @return true if successful
     */
    protected final void decrementControlState() {
        controlStateUpdater.decrementAndGet(this);
    }

}
Revision:	1.11
Committed:	Mon Nov 26 05:59:05 2012 UTC (11 years, 5 months ago) by jsr166
Branch:	MAIN
Changes since 1.10:	+1 -1 lines
Log Message:	javadoc tweaks
#	User	Rev	Content
1	dl	1.1	/*
2			* Written by Doug Lea with assistance from members of JCP JSR-166
3			* Expert Group and released to the public domain, as explained at
4	jsr166	1.6	* http://creativecommons.org/publicdomain/zero/1.0/
5	dl	1.1	*/
6
7			import java.util.concurrent.*;
8			import java.util.concurrent.atomic.*;
9
10			/**
11			* AsyncActions that are always linked in binary parent-child
12			* relationships. Compared to Recursive tasks, BinaryAsyncActions may
13			* have smaller stack space footprints and faster completion mechanics
14			* but higher per-task footprints. Compared to LinkedAsyncActions,
15			* BinaryAsyncActions are simpler to use and have less overhead in
16			* typical uasges but are restricted to binary computation trees.
17			*
18	jsr166	1.11	* <p>Upon construction, a BinaryAsyncAction does not bear any
19	dl	1.1	* linkages. For non-root tasks, links must be established using
20			* method <tt>linkSubtasks</tt> before use.
21			*
22	jsr166	1.7	* <p><b>Sample Usage.</b> A version of Fibonacci:
23	dl	1.1	* <pre>
24			* class Fib extends BinaryAsyncAction {
25			* final int n;
26			* int result;
27			* Fib(int n) { this.n = n; }
28			* protected void compute() {
29			* if (n > 1) {
30	jsr166	1.9	* linkAndForkSubtasks(new Fib(n-1), new Fib(n-2));
31	dl	1.1	* else {
32	jsr166	1.9	* result = n; // fib(0)==0; fib(1)==1
33			* complete();
34	dl	1.1	* }
35			* }
36			* protected void onComplete(BinaryAsyncAction x, BinaryAsyncAction y) {
37	jsr166	1.8	* result = ((Fib)x).result + ((Fib)y).result;
38	dl	1.1	* }
39			* }
40			* </pre>
41			* An alternative, and usually faster strategy is to instead use a
42			* loop to fork subtasks:
43			* <pre>
44			* protected void compute() {
45			* Fib f = this;
46			* while (f.n > 1) {
47	jsr166	1.9	* Fib left = new Fib(f.n - 1);
48			* Fib right = new Fib(f.n - 2);
49			* f.linkSubtasks(left, right);
50			* right.fork(); // fork right
51			* f = left; // loop on left
52	dl	1.1	* }
53			* f.result = f.n;
54			* f.complete();
55			* }
56			* }
57			* </pre>
58			*/
59			public abstract class BinaryAsyncAction extends ForkJoinTask<Void> {
60			private volatile int controlState;
61
62			static final AtomicIntegerFieldUpdater<BinaryAsyncAction> controlStateUpdater =
63			AtomicIntegerFieldUpdater.newUpdater(BinaryAsyncAction.class, "controlState");
64
65			/**
66			* Parent to propagate completion; nulled after completion to
67			* avoid retaining entire tree as garbage
68			*/
69			private BinaryAsyncAction parent;
70
71			/**
72			* Sibling to access on subtask joins, also nulled after completion.
73			*/
74			private BinaryAsyncAction sibling;
75
76			/**
77			* Creates a new action. Unless this is a root task, you will need
78			* to link it using method <tt>linkSubtasks</tt> before forking as
79			* a subtask.
80			*/
81			protected BinaryAsyncAction() {
82			}
83
84			public final Void getRawResult() { return null; }
85			protected final void setRawResult(Void mustBeNull) { }
86
87			/**
88			* Establishes links for the given tasks to have the current task
89			* as parent, and each other as siblings.
90			* @param x one subtask
91			* @param y the other subtask
92			* @throws NullPointerException if either argument is null.
93			*/
94			public final void linkSubtasks(BinaryAsyncAction x, BinaryAsyncAction y) {
95			x.parent = y.parent = this;
96			x.sibling = y;
97			y.sibling = x;
98			}
99
100			/**
101			* Overridable callback action triggered upon <tt>complete</tt> of
102			* subtasks. Upon invocation, both subtasks have completed.
103			* After return, this task <tt>isDone</tt> and is joinable by
104	jsr166	1.5	* other tasks. The default version of this method does nothing.
105			* But it may be overridden in subclasses to perform some action
106			* (for example a reduction) when this task is completes.
107	dl	1.1	* @param x one subtask
108			* @param y the other subtask
109			*/
110			protected void onComplete(BinaryAsyncAction x, BinaryAsyncAction y) {
111			}
112
113			/**
114			* Overridable callback action triggered by
115			* <tt>completeExceptionally</tt>. Upon invocation, this task has
116			* aborted due to an exception (accessible via
117			* <tt>getException</tt>). If this method returns <tt>true</tt>,
118			* the exception propagates to the current task's
119			* parent. Otherwise, normal completion is propagated. The
120			* default version of this method does nothing and returns
121			* <tt>true</tt>.
122			* @return true if this task's exception should be propagated to
123	jsr166	1.10	* this task's parent.
124	dl	1.1	*/
125			protected boolean onException() {
126			return true;
127			}
128
129			/**
130			* Equivalent in effect to invoking <tt>linkSubtasks</tt> and then
131			* forking both tasks.
132			* @param x one subtask
133			* @param y the other subtask
134			*/
135			public void linkAndForkSubtasks(BinaryAsyncAction x, BinaryAsyncAction y) {
136			linkSubtasks(x, y);
137			y.fork();
138			x.fork();
139			}
140
141			/** Basic per-task complete */
142			private void completeThis() {
143			super.complete(null);
144			}
145
146			/** Basic per-task completeExceptionally */
147			private void completeThisExceptionally(Throwable ex) {
148			super.completeExceptionally(ex);
149			}
150
151			/*
152			* We use one bit join count on taskState. The first arriving
153			* thread CAS's from 0 to 1. The second ultimately sets status
154			* to signify completion.
155			*/
156
157			/**
158			* Completes this task, and if this task has a sibling that is
159			* also complete, invokes <tt>onComplete</tt> of parent task, and so
160			* on. If an exception is encountered, tasks instead
161			* <tt>completeExceptionally</tt>.
162			*/
163			public final void complete() {
164			// todo: Use tryUnfork without possibly blowing stack
165			BinaryAsyncAction a = this;
166			for (;;) {
167			BinaryAsyncAction s = a.sibling;
168			BinaryAsyncAction p = a.parent;
169			a.sibling = null;
170			a.parent = null;
171			a.completeThis();
172			if (p == null \|\| p.compareAndSetControlState(0, 1))
173			break;
174			try {
175			p.onComplete(a, s);
176	jsr166	1.3	} catch (Throwable rex) {
177	dl	1.1	p.completeExceptionally(rex);
178			return;
179			}
180			a = p;
181			}
182			}
183
184			/**
185			* Completes this task abnormally. Unless this task already
186			* cancelled or aborted, upon invocation, this method invokes
187			* <tt>onException</tt>, and then, depending on its return value,
188			* completees parent (if one exists) exceptionally or normally. To
189			* avoid unbounded exception loops, this method aborts if an
190			* exception is encountered in any <tt>onException</tt>
191			* invocation.
192			* @param ex the exception to throw when joining this task
193			* @throws NullPointerException if ex is null
194			* @throws Throwable if any invocation of
195			* <tt>onException</tt> does so.
196			*/
197			public final void completeExceptionally(Throwable ex) {
198			BinaryAsyncAction a = this;
199			while (!a.isCompletedAbnormally()) {
200			a.completeThisExceptionally(ex);
201			BinaryAsyncAction s = a.sibling;
202			if (s != null)
203			s.cancel(false);
204			if (!a.onException() \|\| (a = a.parent) == null)
205			break;
206			}
207			}
208
209			/**
210			* Returns this task's parent, or null if none or this task
211			* is already complete.
212			* @return this task's parent, or null if none.
213			*/
214			public final BinaryAsyncAction getParent() {
215			return parent;
216			}
217
218			/**
219			* Returns this task's sibling, or null if none or this task is
220			* already complete.
221			* @return this task's sibling, or null if none.
222			*/
223			public BinaryAsyncAction getSibling() {
224			return sibling;
225			}
226
227			/**
228			* Resets the internal bookkeeping state of this task, erasing
229			* parent and child linkages.
230			*/
231			public void reinitialize() {
232			parent = sibling = null;
233			super.reinitialize();
234			}
235
236			/**
237			* Gets the control state, which is initially zero, or negative if
238			* this task has completed or cancelled. Once negative, the value
239			* cannot be changed.
240			* @return control state
241			*/
242			protected final int getControlState() {
243			return controlState;
244			}
245
246			/**
247			* Atomically sets the control state to the given updated value if
248			* the current value is and equal to the expected value.
249			* @param expect the expected value
250			* @param update the new value
251			* @return true if successful
252			*/
253	jsr166	1.2	protected final boolean compareAndSetControlState(int expect,
254	dl	1.1	int update) {
255			return controlStateUpdater.compareAndSet(this, expect, update);
256			}
257
258			/**
259			* Attempts to set the control state to the given value, failing if
260			* this task is already completed or the control state value would be
261			* negative.
262			* @param value the new value
263			* @return true if successful
264			*/
265			protected final void setControlState(int value) {
266			controlState = value;
267			}
268
269			/**
270			* Sets the control state to the given value,
271			* @param value the new value
272			*/
273			protected final void incrementControlState() {
274			controlStateUpdater.incrementAndGet(this);
275			}
276
277			/**
278			* Decrement the control state
279			* @return true if successful
280			*/
281			protected final void decrementControlState() {
282			controlStateUpdater.decrementAndGet(this);
283			}
284
285			}